1. Field of the Invention
The invention is directed to a therapy apparatus for treatment with focussed ultrasound, comprising a cooled ultrasound source implemented as phased array and a preceding acoustic lens.
2. Description of the Prior Art
A therapy apparatus of the above type is utilized for treating both benign as well as malignant tissue modifications. Temperatures in the range from 40 through 100.degree. C. can be generated in the focus during the treatment, whereby the temperature is selected dependent on the clinical picture to be respectively treated.
The employment of phased arrays for ultrasound therapy is disclosed by German OS 31 19 295 The advantage of employing phased arrays is comprised therein that the focus zone of the ultrasound can be displaced by suitable drive of the phased array without requiring the is displacement of the ultrasound source relative to the subject to be treated.
In order to reduce the number of ultrasound transducer elements of the phased array required in order to enable a specific displacement of the focus zone, a prefocussing with an acoustic lens is provided in European Application -0 214 782, which is directed to a therapy apparatus of the species initially cited. In order to save installation space, the acoustic lens is implemented as a Fresnel lens. At the same time, the Fresnel lens serves as carrier for the ultrasound transducer elements of the phased array, these being attached to the back side of the Fresnel lens facing away from the focus zone. At its front side, the Fresnel lens, which also acts as an acoustic matching layer, is provided with a further acoustic matching layer.
For heat elimination, the Fresnel lens is provided with a cooling channel in the region of its outer edge. Since the cooling channel can only be provided in the region of the edge of the Fresnel lens, the cooling is not very effective. Added thereto is that the realization of a Fresnel lens containing a cooling channel involves rather considerable outlay. The manufacture of the matching layer applied to the Fresnel lens also involves high outlay.
U.S. Pat. No. 4,936,303 also discloses a therapy apparatus with an ultrasound source and a preceding acoustic lens. For cooling the ultrasound source, an ultrasound-conductive coolant adjoining that side of the ultrasound source facing toward the lens is located between the lens and the ultrasound source.
U.S. Pat. No. 4,586,512 also discloses a therapy apparatus for treatment with focussed ultrasound, wherein an ultrasound source executed as phased array is cooled with an adjacent coolant. An acoustic lens is not provided.